1. Field of the Invention
This invention relates to a rotation shaft seal, especially, a rotation shaft seal used to seal high-pressure fluid such as CO2 gas.
2. Description of the Related Art
As a conventional rotation shaft seal, one having a construction shown in FIG. 6 is known. That is to say, a rotation shaft seal, in which a seal elements 33 and 34 made of PTFE and a rubber lip 35 are assembled with an outer case 36, a supporting member 37, and an inner case 38, is widely known (refer to Japanese Patent No. 3346743, for example).
However, in the conventional rotation shaft seal shown in FIG. 6, with recent progress of high-pressurization with cooling media such as CO2, contact pressure P of the rubber lip 35 on a rotation shaft 2 becomes excessive as shown in FIG. 4B, abrasion is developed early, and outer leak of sealed fluid is generated. That is to say, the conventional rubber lip 35 having a thickness dimension W4 approximately same to a tip end 35a is pressed to the rotation shaft 2 with a contact pressure distribution of steep mountain shape. This causes problem in durability.
It is therefore an object of the present invention to provide a rotation shaft seal with which the contact pressure is reduced keeping number of construction parts, abrasion is hardly generated with lubricant oil lead to sliding face, and excellent sealability is kept for a long period of time.